The present invention relates generally to gear systems, and, more particularly, to strain wave gearing.
In general, a strain wave gearing system generally includes a cup-shaped flex gear with an exterior, radially-oriented ring of gear teeth positioned near the rim of the cup and an output hub connected to the base of the cup. Inside of the rim is an elliptically-shaped wave generator with an input hub, wherein the exterior rim of the wave generator has a longer major axis length than a minor axis length. The wave generator elastically deforms the ring of teeth into a corresponding elliptical shape. Surrounding the flex gear is a stationary ring gear with an interior, radially-oriented ring of gear teeth. As the wave generator is rotated in the flex gear, the teeth proximate the major axis of the wave generator engage the teeth of the ring gear, and the teeth proximate the minor axis of the wave generator are drawn in to pass inside of the teeth of the ring gear. The ring gear has more teeth than the flex gear (for example, two more) which causes the flex gear to slowly rotate within the ring gear as the wave generator is rotated rapidly in the opposite direction. Thus, a significant gear reduction is accomplished via a relatively small mechanism.
The configuration and operation of a strain wave gearing system relies on the flex gear being elastically deformable at the ring of gear teeth. But it would be disadvantageous to have the hub portion be similarly flexible because the hub is where the output of the strain wave gearing system is located. To allow flex gear to be flexible in one region and rigid in another, flex gears traditionally have a cup or silk hat shape. Such a shape puts a sufficiently long length of material between the teeth and the hub, allowing the material in the flex gear to elastically deform while minimizing the risk of premature fatigue failure. Unfortunately, this long length increases the overall length of the strain wave gearing system, which can be problematic in applications where space for a gearbox is limited.